<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .normal-div {
            height: 300px;
            background-color: #FEDC00;
        }

        .rel-div {
            position: relative;
           
        }

        .abs-div {
            position: absolute;
            /* left: 10px;
            top: 20px; */
        }
    </style>
</head>
<body>
    <div class="normal-div">
        我用来占位置
    </div>
    <div class="abs-div">我没有设置left/top值，尝试设置left/top试一下。</div>
</body>
</html>